Polymerization of caprolactam with amino acids and the products therefrom



3,937,902 Patented May 29, 1962 3037 002 POLYMERIZATION 6F ,CAPROLACTAM WITH AMINO ACIDS AND THE PRODUCTS THERE- FROM Edward W. Pietrusza, Glenn A. Nesty, and Rudolph Pinter, Morristown, N.J., assignors to Allied Chemical gorporation, New York, N.Y., a corporation of New ork No Drawing. Filed Jan. 14, 1959, Ser. No. 786,690

5 Claims. Cl. 260-78) as for example, phosphoric, sulfuric, hydrochloric acids and the organic acids, such as acetic acid, propionic acid, oxalic acid, toluene sulfonic acid, benzoic acid and many others. Although these materials have been proven to be United States Patent Office operative, each of them affects the reaction in an undesirable manner. The compound may, for example, be an excellent catalyst but also an excellent chain terminator thereby limiting the degree of polymerization, or the compound may be a good catalyst but undesirable in that it cannot be removed from the end product, thereby imparting to it undesirable degradative effect-s. Finally the compound may possess activity without undesirable side effects, but may be too slow in its action to be of commercial value. p v I v It is accordingly an object of this invention to provide catalysts for the polymerization" of caprolactam which possess sufiicient activity to be of commercial value but which do not produce any undesirable reactions, such as unwanted chain termination, degradative effects or discoloring. i I I g It is a further object of this invention to provide catalysts which will not only catalyze the reaction but will have the ability to copolymerize with the parent substance without deleteriously atfecting the properties of the parent polymer. v

A further object of this invention is to provide catalysts which do not requrie the additional presence of water.

A further obje ct of this invention is to provide c0- polyamide compositions that can be melt-spun into fibers possessing superior tensile properties, and with melt points higher than the parent polycapramide; also to provide a copolyamide composition with enhanced stability at elevated temperatures. it has now been found that these objects and other advantages incidental thereto can be attained with the use of a mono substituted methylamine in which the substituent is a 6-carbon ring free from aliphatic unsaturation joined to the methyl carbon and containing on a ring carbon a single carboxyl group, the longest chain joining the amine nitrogen andthe carboxyl group containing from 9 to 13 total atoms.

It has been found that these amino acids as initiators and/or catalysts for the polymerization of caprolactam are sufliciently active to be of a commercial value. They do not terminate polymerization of the caprolactam and therefore can be used in the manufacture of both spinning and molding grade polymers. Furthermore, they are completely incorporative with caprolactam and therefore, after having performed their function as catalysts, disappear by copolymerizing with the parent monomer without deleteriously affecting its properties, and may be effectively used with anhydrous caprolactam. These characteristics make these high-melting non-volatile compounds particularly desirable for use in a continuous polymerization process. Furthermore, it has been found that the copolymeric compositions formed by the reaction with caprolactam of these acids, particularly benzylamine-4- carboxylic acids, in percentages varying from 199% are of considerable commercial value and that the compositions containing 2050% by weight of the amino acid, particularly that mentioned above, have substantially higher 'heat stability, higher tensile modulus and higher melting point properties than the caprolactam homopolymers.

The mono substituted methylamine carboxylic acids of the invention are distinguishable from other amino acids in that'they appear to satisfy the following requirements for a good catalyst and initiator for polymerization of caprolactam 1) they do not cyclize and form stable endgroups (-chain termination), (2) they are practically neutral but tend to be slightly on the basic side (3) both functional groups, i.e., the amino and carboxylic acid group, are of suflicient strength to enable smooth co-polymerization with the parent monomer (4) the mono substituted methylamine carboxylic acids are similar to omega amino caproic acid in molecular structure so that they fit into the framework of the parent polymer and thereby become incorporative (5) the amino grouping is not attached directly to a ring structure.

Examples of the invention include the following: benzyl amine-4-carboxylic acid and its monohydr-ate salt, amino methyl cycloheXane-4-carb0xy1ic acid, and benzyl amine-S-carboxylic acid.

While other amino acids have molecular structures which are somewhat similar to omega amino caproic acid, they do not meet all of these requirements and consequently fail to meet the high standards which distinguish these catalysts and initiators from those of the prior art.

EXAMPLE 1 Four parts by weight of benzyl amine-4-carboxylic acid was introduced with. an initial charge of 400 parts of E-caprolactam and 40 parts of water into a reaction vessel, provided with a condenser and an agitator. The mixture was Wellmixed in a nitrogen atmosphere and brought to a temperature of C. after which the temperature was raised to between 200 and 210 at atmospheric pressure in three hours while cooling the condenser with cold water. The temperature was held at this point for an additional hour whereupon steam was substituted for the' cold water as the coolant in the condenser and the temperature brought up to 260 C. at atmospheric pressure in about 2 /2 hours and maintained at 260 C. and atmospheric pressure for 10 hours. The course of the polymerization was observed by periodically withdrawing samples and measuring viscosity of unwashed samples after the temperature had been raised 3 to 260 C. Viscosity measurements were made in mcresol at a 0.50% concentration at 25 C.

The above example was repeated, varying only the amount of benzyl amine-4-carboxylic acid introduced. The resulitng viscosity measurements obtained are set forth in the following table:

Benzyl Amine-4-Carb0xylic Acid Reduced Viscosity =Nn after Following Number of Hours on Temp. (260 0.) Cone. BAA-CA) Wt. Percent 1 Introduced as its monohydrate salt. The reduced viscosity, N R= (Time of eifiux of solution divided by time of effiux of solvent from same orifice) -1, all divided by concentration or solution expressed as grams of polymer per 100 cc. of solvent.

The relation of average molecular weight to reduced viscosity is given by the equation of H. Staudinger and H. Schnell (Malrromolekulare Chemie of 1947, vol. 1, pages 44-60):

Average molecular weight=N 13,500

Thus, average molecular weight of the polymer with an N value of 2.57 is about 34,700.

EXAMPLE 2 This example was carried out by the procedure of Example 1 except that aminomethyl cyclohexane-4-carboxylic acid was used in the place of benzyl amine-4-carboxylic acid.

The reduced viscosity measurements obtained with the use of aminomethyl cyclohexane-4-carboxylic acid are set forth in the following table:

Aminomethyl Cyclohexane l-Carboxylic Acid Reduced Viscosity after Following Number of Cone. AMC-4-CA, Hours on Temp. (260 C.)

Wt. Percent EXAMPLE 3 This example was carried out by the procedure of Example 1 except that benzyl amine-:l-carboxylic acid was used in place of benzyl amine-4-carboxylic acid.

The reduced viscosity measurements obtained with the use of benzyl amine-S-carboxylic acid are set forth in the following table:

Benzyl Amine-3-Carb0xylic Acid 4 EXAMPLE 4 Four parts by weight benzyl amine-4-carboxylic acid as its monohydrate salt was introduced with an initial charge of 400 parts of anhydrous e-caprolactam into a reaction vessel provided with a condenser and agitator. The mixture was well mixed in a nitrogen atmosphere and brought to a temperature of C. after which the temperature was raised to between 200 and 210 C. at atmospheric pressure in three hours while cooling the condenser with cold water. The temperature was held at this point for an additional hour whereupon steam was substituted for the cold water as the coolant in the condenser and the temperature brought up to 260 C. at atmospheric pressure is about 2% hours and maintained at 260 C. atmospheric pressure for 10 hours. The course of the polymerization was observed by a periodic withdrawal of unwashed samples and viscosity measurements after the temperature had been raised to 260 C. Viscosity measurements were made in m-cresol at a 0.50% concentration at 25 C.

The above experiment was repeated, varying only the amount of benzyl amine-4-carboxylic acid introduced. The resulting viscosity measurements obtained are set forth in the following table:

Reduced Viscosity after Following Number of Cone. Benzyl Hours on Temp. (260 C.) Arnine-4-carboxy1ic Acid, wt. percent 1 Introduced as its monohydrate salt.

From the above examples it can be seen that if water is used as an initiator of the reaction only trace amounts of these amino acids are required to effect rapid polymerization of caprolactam. The best polymerization rates (1 to 3 hours heat-up, and 0.00 to 5 hours on temperature) are obtained with amino acid concentrations of 0.25 to 1% in the presence of about 10% of water. When water is not used as an initiator, the best rates are obtained with amino acid concentrations of about 3% to about 10%. At these reaction rates spinning grade polymers can be obtained after about 0.00 to 1 hour on temperature with a heat-up time of 1 to 3 hours. If chain termination is desired, it can be realized by introducing steam. High molecular weight molding grade polymers can be obtained after 5 to 10 hours on temperature with 1 to 3 hours heat-up, provided a good inert gas sweep of nitrogen or carbon dioxide is utilized. It is noteworthy that these amino acids function as catalysts and initiators in the early stages of the polymerization, and then disappear by incorporation with the parent polymer. Consequently, after a certain time elapse, molecular weight candue to their presence since in not he expected to increase a sense they are swallowed into the framework of the polymer. Molecular weight increase thereafter is eifected by the dehydrating affects of gas sweep, or reduced pressure.

When aminomethyl cyclohexane-4-carboxylic acid or benzylamine-3-carboxylic acid is used as the catalyst in the polymerization of anhydrous caprolactam, good polymerization rates are obtainable with concentrations of the amino acid between 3% and 10% by weight, substantially as shown in Example 4 for the benzylamine-4-carboxylic acid monohydrate. It has furthermore been found that these catalysts do not terminate polymerization of the caprolactam and therefore can be used advantageously in the manufacture of both spinning and molding grade polymers.

The following tables illustrate the typical fiber proper- 3,037,002 A 5 a ties and spinning results of some of the copolyamides Although certain preferred embodiments of the invenobtained when larger amounts of the amino acids were tion have been disclosed for purpose of illustration, it used in the production of copolymers using the method will be evident that various changes and modifications of Example 1. may be made therein without departing from the scope 5 and spirit of the invention. Poly- Instron Initial We Chum: Polyamide Composition, amide, 111115;, Tensile 1. The process for polymerizing caprolactam compris- Wt. percent 021.5 Denlel' UE U'rs E 3 heating said lactam at temperatures in the range fi g df between about 180 and about 300 C. at pressures not 10 substantially exceeding atmospheric in the absence of sub- Benzyl An1ine -4-Carstantial elemental oxygen and of more than about 1% m gi; Acld/Capro" total Water in the presence of 0.25% to 10% by weight 7 Non-gpjnnablg of the mixture of benzlamine-S-carboxylic acid, conggi g; g8 tinuing said heating at least until a polymer product has 4 135 24 60 1 an average molecular weight above about 5000.

fig g-g 2. The process for polymerizing caprolactam compris- 209 97 27 5'8 50 ing introducing said lactam into a reaction vessel along 10 so 212 167 29 6 0 46 4 0/100 (NO) 222 123 19 5.7 30 41 wlth about 10% by weight of water, heating sa1d lactam Aminomethyl Cycloat temperatures 1n the range between about 180 and t y 20 about 300 C. at pressures not substantially exceeding c1d/Oapr0lactam. 100 0 370 Non-spinnable atmosphenc 1n the presence of 0.25 to 1% by weight of 3% 2:2 2} benzyl amine-3-carboxylic acid, continuing said heat- 222 71 27 6.3 43 ing at least until a polymer product has an average molecgig ii g? ular weight above about 5000.

3. The process for polymerizing caprolactam comprising heating said lactam at temperatures in the range be- When monofilament Samples of P Y Wfire tween about 180 and about 300 C. at pressures not wound on Plastlc 5139013 and Plaiied 111 clrcu-latlllg substantially exceeding atmospheric in the presence of oven for 24 11 1 0 at and the following 2050% by weight of benzyl amine-3-carboxylic acid, results were obtalned. The O s gnifies a non-catacontinuing said heating at least until a polymer product lyzed polycapramide, polymerized in the presence of 10% has an average molecular weight between about 5000 and water. 50,000.

Original Final Percent Polymer U.S.T.

Den. U.E., U.T.S., 'I.M., Den U.E., U.'r.s., T.M., retained percent g./d. g./ l. percent g./d. g./d.

10% 1314-4-04 167 29.0 6. 04 46.4 152 14.4 4.26 59 70 20% BAA-GA" 07 26.7 5.81 50.0 85 15.6 4.56 55 79 30% BA4-OA 94 21.3 6.80 54.0 112 19.4 5.45 58 94 BA4CA 135 23.7 5.65 60.2 142 16.4 4.15 73 10% AMO-4-OA 87 25.5 7.13 36.4 84 9.8 2.53 50.1 36 20% AMo-4-0A 71 27.3 6.26 42.8 72 10.1 2.47 51.6 39 30% AM0-4-oA 75 22.9 5. 62 40s 70 9.9 2.14 50.8 as 40% AMC-4-OA 69 24.4 5. 51.2 67 10.1 1.88 59 32 Nyl0n6-NO 123 10.0 5.71 41.4 127 6.3 2.07 58 36 The polyamides derived from the reaction of 2050% 4. A two component linear copolyamide of benzyl by weight of benzyl amine-4-carboxylic acid with caproamine-3-carboxylic acid and caprolactam. lactam are particularly well suited for fiber spinning and 5. A two component linear copolyamide of benzyl tire cord use. The approximate range of suitable molec- 5 amine-3-carboxylic acid and caprolactam in which 20- ular weight for these materials lies within the range 0 50% by weight of the copolyarnide is derived from benof 7-30,000. zyl amine-3-carboxylic acid.

The polyamides derived from the reaction of 2050% by weight of benzyl amine-3-carboxylic acid, and amino e r nces C ted in the file of this patent methyl cyclohexane-4-carboxylic acid with carprolactam UNITED STATES PATENTS are particularly well adapted 'for use in extrusion injection molding and as a plastic film or coating. The ap- 2,868,769 Graham Jan. 13, 1959 proximate range of suitable molecular weights for these 2,910,457 Teniin et a1. Oct. 27, 1959 materials is slightly higher extending up to about 50,000. 

1. THE PROCESS FOR POLYMERIZING CAPROLACTAM COMPRISING HEATING SAID LACTUM AT TEMPERATURES IN THE RANGE BETWEEN ABOUT 180* AND ABOUT 300*C. AT PRESSURES NOT SUBSTANTIALLY EXCEEDING ATMOSPHERIC IN THE ABSENCE OF SUBSTANTIAL ELEMENTAL OXYGEN AND OF MORE THAN ABOUT 1% TOTAL WATER IN THE PRESENCE OF 0.25% TO 10% BY WEIGHT OF THE MIXTURE OF BENZLAMINE -3-CARBOXYLIC ACID, CONTINUING SAID HEATING AT LEAST UNTIL A POLYMER PRODUCT HAS AN AVERAGE MOLECULAR WEIGHT ABOVE ABOUT
 5000. 